Tunable magnetron



1 Feb. 17, 1948.

P. SPENCER TUNABLE MAGNETRON Filed June 2, 1944 2 Sheets-Sheet 2 Patented Feb. 17, 1948 UNITED STATES PATENT ornc'e TUNABLE MAGNETRON Application June 2,1944, Serial No. 538,423

10 Claims.

This invention relates to an electronic discharge tube of the type adapted to generate ultrahigh frequency oscillations and more particularly to one in which the frequency of one or more resonant circuits within the tube determines the frequency of the oscillations produced.

In devices of. the type to which the invention relatesthe resonant circuit may be provided by one or more resonant chambers or cavities having inductance and capacitance and thus constitutinga tuned circuit, the frequency of which is determined by the dimensions and geometry of the internalstructure.

In some applications of devices of the type to which the invention relates, it is desirable to vary within limits the frequency of the oscillations generated by the tube. Heretofore it has been difiicult to provide for such variation at the will of the operator since the resonant circuit which determines the frequency generated is disposed entirely within the tube, and in order to vary one of 'the circuit parameters determining "the frequency generated, .it has been the practice to provide some movable element within the tube. By varying the position of the movable element, the resonant frequency of the resonant chamber or equivalent resonant circuit of the tube is varied and accordingly the frequency of the oscillations generated is varied. The use of such a movable element greatly complicates the tube structure and since the element must be actuated from the exterior of the tube, some means must be provided for transmitting motion to the element through the exterior wall of the tube as, for example, by making a portion of the tube wall flexible. This further complicates the tube structure.

It is among the objects of the present invention to obviate the above-mentioned difficulties by providing a means wherebythe frequencies generated may be controlled from a point externally of the tube and without mechanical motion therein.

It is a further object of the invention to provide a device of the type described which permits the high voltage elements of the system to be regulated inside of the evacuated portion of the tube. thus preventing the possibility of arc-over which would bepresent if the high voltage elements were provided with connections extending externally of the evacuated space of the tube.

It is a further object of the invention to provide a device of the type described in which changes in the adjustment of the tuning means maybe effected at highspeed so that the frequencies generated by the tube may be changed very rapidly to effect a continuous periodic variation in the frequencies generated.

The above and other objects and features of s -the invention will be fully set forth in the following detailed description, taken in conjunction with the accompanyingdrawings in which:

Fig. 1 shows a longitudinal section through a magnetron constructed in accordance with my :rinvention; Fig. 2 shows a section taken Fig. 1;

Fig. 3 shows a section through the tuningde vice of the tube shown in the preceding figures -;"and is taken on line Y-Y of Fig. 1;

Fig. 4 shows a fragment of a magnetron of the type shown in Figs. 1 and 2but modified tuning means;

Fig. 5 shows a fragment of a magnetron of the type shown in Figs. 1 and 2 provided with a further modified tuning means;

Fig. 6 showsa section taken on line Z-Z of Fig. 5;

Fig. 7 shows aside elevation; and

Fig. 8 shows an end view of a tuning ring of the type shown in Figs. 4 and 5 and suitable for use with the tuning means of any of the forms of the invention shown.

Referring to the drawings and first to the form shown in Figs. 1, 2 and'3 thereof, thereis shown a magnetron comprising a block I of conductive material such as copper. :The block I forms the anode and, in the instance shown, constitutes a portion of the'envelope of the magnetron. The vblock l is provided with hollow end sections 2 and 3 covered by end caps 4 and. 5 likewise of.

conductive material. Between the. hollow end sections 2 and 3 is located a central bridgingpon; tion. 6, having a central bore 1 within whicha cathode 8 is centrally supported by a pair of 40 lead-in conductors 9 and "3. The conducto'r 9 is sealed through a glass seal l l mounted at the secured within the wall of the block I adjacent the upper hollow end section 2. The lead-in conductor I ll is likewise sealed through a. similar glass seal and pipe, not illustrated, adjacent the lower hollow end section 3.. A plurality of radial slots [3 extend from the bore 1 and each of the slots terminates in a cavity l4 extending through the bridging portion 6. In this way the anode structure is provided with a plurality of wedge shaped arms l5. the faces of which cooperate as anode sections with the cathode 8. Suitable magnetic poles l6 and I! are provided adjacent the on line X-X of provided with a i passes through a glass seal 20.,mounted atthe outer end of aconductive pipe 2l hermetically sealed through the wall of the block I. exterior of the tube the high frequency oscilla-f On the H tions may be conducted to any suitable utilization V circuit by a concentric line or any other trans mission means in a manner known, in.the.art..-

In the operation of suchdevices a capacity exists between the cathode 8 and the face of each" anode section I5. Also capacitances exist between x the side walls of each of the slots" 13. The inner walls of the cavities l4 constitute inductances. The anode therefore is so designed and spaced atire h catbodet at t e cap and inductances described constitute circuits which are tuned. ,Theconstruction 5 0 .far described is such that these circuits are resonantat a predetermined frequency depending uponthegeometry of the tube The device is intended to operate so that each cavity l 4 and, its adjacent. arms form a circuittuned to the frequency at .which each of the other cavities l4 and its adjacent arms oscillate. V

Devices of the type described may oscillate. not.

only .in the desired mode,- corresponding to the desired frequency, but .mayalso, oscillate .in .certain spurious modes, corresponding to vundesired frequencies. For example, oscillationsmayoccur betwecnnon-adjacent arms, 15 and to limit such spurious or undesired oscillations alternate arms l5 may be connected together. .Inthe in. stance shown, such interconnection is efiected by means of straps 22 and..23,. theupperustrap. 22

being connected.v to alternate arms I Band free from contact with the intervening arms which are provided with slots 24 through which the strap .22 may. pass without ,contactingsuch inter vening, arms. The lower strap 23 .isconnectedlto the. intervening armsandis not. connected.to the. alternate arms, free passage'therethroughbeing permitted by similarslots .24..insaid alternate arms.. Thisconstruction serves to limit'the spue. rious. oscillations. in 1 a manner morefullyudis closed .in my .copending. applications, SerialNo. 465,413, filed .November ,13,..1942,;and..Serial No- 421,145, filed December 1, l94l,,now.Patent.No..

Heretofore where. attempts have .been made to vary the. frequency at which thefianodestructure tends to .oscillate..some tuningmemb'er disposed within .the tube body adjacent the anode arms 15.

has beenmoved towardor awayxfromth'e arms,

in order to vary the, effective capacitance. .of. the.v r na t i cuits-i h sbas re ui e ome means such we x l d a ra m .f rm een a fl of the tubeand permitting movement of the tun;

l'm m it aiii o ihaans s ea e 1-.-

In-this I construction. the desired tuning effect is obtained',by. providing. conductors .25. and. 26'; connectedrespectively to .the'straps 22 land 23, i which conductors extend outwardly throughbne of the slots 13 anditscorresponding cavity l d and through. a conductive pipe 21. 'The pipe 2'! is hermetieallyisealed within the wall of the block;

l and is'closed at its outer end eyeg ass seal 28. The s eal'28 has a; tubular portion extending for e u siaai a s i s ie iihere a 'i il pipe 21, and the conductors 25 and 26 terminate in metallic strips 29 and 30 within the tubular portion of the seal 28. The metallic strips 29 and 30 constitute condenser plates which provide additional capacitance connected in the resonant circuits provided by the anode structure. This capacitance is therefore a portion of the capacitance determining the frequency at which each oscillatory circuit is resonant. Inforder to alter the capacitance of the oscillatory circuits, and thereby alter the frequency at which these circuits resonate, a conductive sleeve 3| constituting a tuning ring is provided surrounding a portion of theseal 28 and enclosing the plates 29 and 30. Thetuning ring 3] is mounted for movement rela- 'tiveftothe plates 29 and 30. In the instance shown in Figs. 1, '2 and 3, the sleeve is reciprocable in. a direction extending longitudinally of the plates}? and 30.

Iri'operation, by shifting the tuning ring 3| in a longitudinal direction so that a greater or lesser portion of its surface area is opposed to the con- V denser plates .29 and 30,- -the. lectric field provided by the plates is altered. Accordingly-the capacitance of the oscillatory circuits in which these plates are connected is altered and the fref quencies at which the oscillatory circuits resonate are varied. Increases or decreases in the effec:

tive capacitance of the oscillatory circuitresult, respectively, in lower or higher frequenciesof the v oscillations generated by theitube' The frequencies of the oscillations generated ma therefore be. controlled, within limits, at the will of the operator while the tube is in operation.

It will be observed that the invention provides a device in which the 'control of' the oscillations generated is enacted without mechanical motion of any element within the tubealthough the liighi voltage elements of the system remain'inside of the evacuated space. By this construction'the difficulties encounteredwhere it is attempted to I effect motion of some element within the tube,

through a flexible wall thereof are avoided' Also there is no danger of arcing which would be pres-j ent if similar tuning means were b-roughtjout' through glass seals and usedunder atmospheric conditions.

It will be apparent that the tuning sleeve may be adjusted either manually or' mechanically to secure desired adju'stments or variationsiin'the frequencies of the oscillations generated; Wh'ei-et: it is desired to vary thefrequencies "periodicallylf the sleeve may beactuated a't time rate. 1

In theform of theinvention described in the 'foregoing, the conductors 2'5' ai1di26ffare con -f. nected to the straps 22 -and23I- 'Alternative con -Q structions maybe used; forexampleItheconducr tors maybe connected directly" to adjacent arms v I I5 as showri'in 'Fig.'4.'- In-this figure therelis shown a portion of a magnetron which is similar to the-magnetron shown 'ir'i' Fig's. l, 2 and 3. In

this instance the conductors 25 and 26 are' co n nect ed directly to adjacent arms l5.

vided'with anystrapping means:

Inboth of the constructioiis'lso far described 7 While there is'shown'i'n thisfig ure a strapping means 22,- it willbe' understood that thisf strap performs its usual functions" and "is not directly COI'ilIleCtd' toone or the otherbfjthe conductors it has been found de'sir'able'to ma e the effective nection of conductors 25 and 26 and the center of the condenser provided by the strips Hand-30 approximately equal to-NA/2 where A is the length of the waves on the system and N is a small integ'en- It ,ciprocable, the tuning sleeve'3l may be so constructed that rotation thereof will alter the effecbe understood that insteadotbeing retive capacitance of the condenser. For example,

the sleeve 3| may be provided with slots 32 as shown in Figs. 7 and 8 extending longitudinally thereof so that the surface area of the sleeve jcoacting with the condenser plates 29 and 30 may be altered by angular adjustments of the sleeve 3 I. This construction isparticularly adapted for continuous operation to periodically vary the frequencies of the oscillations generated, the sleeve being rotated at a predetermined speed. In both forms of the invention describedin the foregoing, a pair of conductors 25 and 26 is provided, which conductorsare of the sameelectrical length and constitute a balanced transmission line. In some instances, as for example in the construction shown in Figs. and 6, the connections tothe condenser plates 29 and 30 may not provide a balanced transmission line. In these figures there'is shown a; magnetron which is generally similarto that shown in Figs. 1, 2 :and 3 except that the connections between the bridging portion 6 and the condenser plates have been modified. a

In; this construction oneof the conductors-25 is connected to the strapzz and extends outwardly through the free space 2 and through the conductive pipe 21 to the condenser plate 29.

The pipe 21 is hermetically sealed within the wall.

of the block I and in this instance opens into the free'space 2. A choke section. 35 having one end connected to the pipe 21 at a point intermediate the length thereof extends parallel \to and is spaced from the outer end of the pipe. The glass seal 28 is in this instance sealed to the outer end of the choke section 35. The condenser plate 30 is connected directly by the conductor 26 to the outer end of the conductive pipe 21. The length of the choke section is approximately equal to M4 where A is the'length of the waves onthe system. As in the previously described construction the condenser plates -29 and 30 are positioned to coact with a tuning ring M on the exterior of the glass seal 28. The provision of a choke section 35 transforms the otherwise unbalanced transmission line resulting from this arrangement to a balanced transmission line and isolates the external part of the tube box from the high frequency of the internal oscillatory circuit.

In all the constructions illustrated the invention is applied to an electronic discharge tube of the type having a plurality of resonant cavities. It will be understood that in its broader aspects the invention is readily applicable to tubes of the type containing a single resonant cavity and the invention may be readily applied thereto by those skilled in the art from the teachings thereof.

While I have described particular embodiments of my invention, it will be apparent that various changes may be made without departing from the teachings hereof. For example, from the embodiments shown, it will be apparent to those skilled in the art that the conductors 25 and 26 may be connected in the oscillatory circuit of the cavity structure in various ways and that the invention may be applied to any tube of the type having an internal oscillatory circuit. While the invention has been described in conjunction with oscillations. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art. a i

. What is claimed is:

1. A tunable electron-discharge device. comprising: an evacuated anode structure having a dielectric wall portion; said anode structure defining at least one cavity resonator; a pair of condenser elements connected to points adapted to be at difi'erent relative potentials in at least one such cavity resonator; said condenser elements being disposed within said anode structure, adjacent said dielectric wall portion; and means, external of said anode structure, and capacltively adjustable with respect to said condenser elements through said dielectric wall portion, for altering the capacitance between sai condenser elements.

2. A tunable electron-discharge device comprising: an evacuated anode. structure defining at least one cavity resonator; a hollow, dielectric member opening into the interior of said anode structure; a pair of condenser elements, disposed within said dielectric member, and connected to points adapted to be at diflferent relative potentials inat least one such cavity resonator; and means, external of said anode structure, and capacitively adjustable with respect to said condenserelements through said dielectric member for altering the capacitance between said condenser elements.

3. A tunable electron-discharge device comprising: an evacuated anode structuredefining at least one cavity. resonator; a hollow, dielectric memberopening into theinterior of said anode structure; a pair of condenser elements, disposed within said dielectric member, and connected to points adapted to be at difi'erent relative potentials in at least one such cavity resonator; and a conducting sleeve, movably mounted exteriorly of said dielectric member, and capacitively adjustable with respect to said condenser elements through said dielectric member, for altering the capacitance between said condenser elements,

4. A tunable electron-discharge device comprising: an evacuated anode structure having a dielectric wall portion; said anode structure defining at least one cavity resonator; a pair of condenser elements connected to points adapted to be at different relative potentials in at least one such cavity resonator by a transmission line having an effective electrical length approximately equal to NW2, where N is a small integer and A is the mean wave length of the oscillations adapted to be generated by said device; said condenser elements being disposed within said anode structure, adjacent said dielectric wall portion; and means, external of said anode structure, and capacitively adjustable with respect to said condenser elements through said dielectric wall portion, for altering the capacitance between said condenser elements. I

5. A tunable electron-discharge device comprising: an evacuated anode structure defining at least one cavity resonator; a hollow, dielectric member opening into the interior of said anode structure; a pair of condenser elements, disposed within said dielectric member. and connected to points adapted to be at difierent relative potentials in at least one such cavity resonator by a transmission line having an eirective electrical asst-gees length approximately equal" to NA/2, where N is a smaliinteger and x isthe'mean wavelength of the oscillations adapted to be: generated by: said deviceyand means. external-of said anodestructure, andcapacitively adjustable with respect to Y condenser elements through said dielectric member, for altering the capacitance between-said condenser elements. Y

6. A tunable electron-discharge device comprising: an evacuatedIanode structure defining at least one cavity re's'onator a hollow, dielectric member opening into the interior of said anode structure; a' pair of condenser elements; disposed within said'dielectric member, and connected to points adapted to beat diiferent relative potentials inat least one such cavity'resonator by a transmission line having an effective electrical length approximatelyzequal to NA/2, where-N is a small integer and x is the mean Wave length of the 1 oscillations adapted to be generatedby I said device; and a. conducting sleeve,- movably mounted exteriorly of said dielectric member, and capacitively adjustable with respect to said condenser elements through saiddielectri'c member for alteringthe capacitance between said condenser elements.

7: Atunable electron-discharge device comprising: -"an*evacuatedfanode structure having a dielectric wall portion; said anode" structure defining a=pluralityof cavity'resonators; a pair of conducting straps alternately contacting successive points of opposite potential in said cavity resonators; a pair of condenser elements "connected, respectively, tosaid straps; said condenser elements being disposed within said anode structure; adjacent said dielectric wall portion; and means, external of said anode structure, and capacitively adjustable with-respect to said condenser elements through said dielectric wall portion, 'for altering the capacitance between said condenser elements.

8. A tunable electron-discharge device 1 comprising: an evacuated anode structure defining a pluralityof cavity resonators: a pair of con ducting straps alternately*contacting successive points of opposite potential'in said cavity resonators; a hollow, dielectric member opening into the interior of said-"anode structure; a pair of condenser elements} disposed within said dielectric member; and'connectedto oneof said straps and-said anode structure by an unbalanced transmission line; a choke sleeve surrou'ndingsaid transmission line to balance the sameyand means, external of 'said anode structure; and

capacitively adjustable with respect 'to' said con:

denser elements throughsaid dielectric Wallportive potentials within said cavity resonator, and

extendingexteriorly of said 'c'e'kvity resonator, condenser elements connected to said conducting members exteriorly of said-cavity resonator: and means; adjacent said condenser elements and capacitively adjustable with respect thereto, for altering the capacitance therebetween.

10; A"tunableelectron-discharge device comprising: an evacuated anode structure including a' cavity resonator; conducting members, connectedto points adapted to be at different relative potentials within said-cavity resonator, and extending-exteriorlv of said cavity resonator; condenser elements connectedto said conducting members-'exteriorly of said cavity resonator; and a conducting sleeve,=spaced from and-surrounding said condenser elements, and capacitively a'd justable with respect thereto, for altering the capacitance therebetween.

' PERCY L.'SPENCER.

IREFERENCESTCITED The following references are of record in the file" of this patent:

1 UNITED STATES PATENTS Number Name Date 2,285,662 Hutcheson June 9, 1942 2,293,387 Haefl Aug. 18, 1942 2,044,369 Samuel 1June'l6, 1936 2,222,902 Hahn .Nov. 26,1940 2,351,744 Chevigny June "20, 1944 2,259,690 Hansen et al. Oct. 21, 1941 2,281,935 Hansen et a1. May 5, 1942 

